In connection with certain well bore operations such as drilling, milling etc. it is required to perform clean-up operations to remove metal debris, i.e. metal chips, shavings remaining in the well. Such debris may otherwise interfere with the proper function of the Blow-Out Preventer (BOP), or other valves present in the well. Metal debris must also be removed before a depleted well is finally plugged to avoid metal debris in the cement plug.
Presently, metal debris is commonly removed by running a downhole magnet into the well. Metal debris is attracted to the magnet. When the magnet has attracted a certain amount of metal debris its magnetic field is weakened and is no longer able to attract further debris. To continue the clean-up operation, the magnet must be returned topside to manually remove the metal debris. After debris removal, the magnet may again be run into the well.
After certain well operations it is necessary to clean the well of metal debris. The requirement may for instance be that less than 0.5 kg of metal debris should remain in the well after clean-up. To fulfil such requirements, a prior art downhole magnet must commonly be run into the well, and returned topside, multiple times. Such operations are time consuming and, consequently, very costly.
The goal of the present invention is to provide a tool for removal of metal debris, which would alleviate or avoid at least some of the disadvantages of the prior art methods and tools.